1. Field of the Invention
This invention relates to electronic circuits, and more particularly to fire alarm control and emergency communication systems.
2. Description of the Prior Art
The discovery of fire by mankind marked the dawn of civilization. From that time to the present, man has benefited by the use of fire. Each year many fires will start accidentally or become out of control causing a great deal of human suffering and possible human death and/or a large amount of property damage. Fire alarm control systems have been developed to protect people and property. Typical prior art fire alarm control systems consisted of a master controller which usually had indicator lights, control switches and power for the entire system.
The master controller was connected to the systems inputs, i.e., smoke detectors and manual pull stations. The master controller made all the decisions regarding how the system was going to respond to various patterns of inputs and the master controller activated or controlled all system outputs. The master controller was wired directly to each of the aforementioned input devices, or wired to a slave device, i.e., a data gathering panel which was wired to the input devices. If there was no danger present, the master controller would communicate with the input that was located at the first address, and the input device located at the first address would communicate its status to the master controller. Then, the master controller would communicate with the input that was located at the second address and the input device located at the second address would communicate its status to the master controller. This sequential process would continue until all the addresses were serially polled. When the master controller received an answer from the input device located at the last address, the master controller would go back to the first address and ask the input device located at the first address for its status. The foregoing process would continue adinfinitum.
In the event one of the input devices detected a possible dangerous condition, i.e., smoke in the third floor, the master controller would have to decide whether or not to process that input immediately or whether to wait until it communicated with the entire system and determined the status of all the inputs. If the master controller elected to process the input response immediately, it might tell the people located on the third floor to evacuate the building, cause fresh air to be circulated on the third floor, and warn the people located on the second and fouth floors of a pending emergency. By processing the first received dangerous condition signal immediately, the master controller would not known that the fire was located on the fifth floor. The master controller may ring an evacuation signal on a floor that does not have to be evacuated at that moment, increasing the danger and possible panic that may result when a floor that should have been evacuated was not evacuated. The reason for the above is that in many fires smoke may leak up a stairwell or be moved by the air handling system. Typically more people die from smoke inhalation than burns caused by fire, so improper air handling may be diastrous. Thus, the master controller risked implementing the wrong response or an incomplete partial response. If instead of reacting immediately to the input devices report of a possible dangerous condition, the master controller polled all the remaining inputs to the system to be sure that it had a new complete picture of the conditions of the building so that its response would more likely be correct, the master controller would take significantly longer before it acts. The basic fact about any fire condition remains: the faster an emergency condition can be detected and measures taken to control the fire, the more efficiently the danger can be controlled. Thus, one of the problems of the prior art was that if the master controller processed an input indicating an abnormal condition immediately it risked the incorrect response or activating its responses in the improper time sequence. Furthermore, if the master controller continued receiving new inputs its response was slower. The foregoing prior art problems became more severe as the buildings in which we live, work, and are entertained in become larger, taller, multi-towered or more spread out like a large shopping mall, university campus or hospital complex.
Another problem of the prior art was that the total status of the building or buildings could only be determined at one location, i.e., the location of the master controller. The master controller may not be located near the entrance that the firemen arrive, or if the master controller was consumed by fire or made inaccessible because of the fire, the entire fire alarm system would not operate.
Another problem of the prior art was that since the input devices were serially connected to the master controller, the failure of any point on the serial link would cause the failure of all remaining input devices connected to that link.
A further problem with the prior art was that there was a limit to the number of input devices that could be connected to a given master controller. Thus, it might be very expensive or impossible to expand a prior art fire alarm system to accommodate future needs.
An additional problem of the prior art was that it was necessary to decide whether a fire alarm systems inputs would be multiplexed or full wired. Installaton costs of prior art fire alarm systems typically equaled hardware costs. By reducing the number of wires in a system the cost of the wire and the cost of drawing the wire would be reduced. Hence, multiplexing techniques were used to reduce the total cost of the alarm system. In the same prior art system some inputs could not be multiplexed and other inputs hard wired.